System and method for producing fertiliser granules
Patent Information
- Application Number
- EP2023833805
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-03-17
- Filing Date
- 2023-12-19
- Publication Date
- 2026-01-21
AI Technical Summary
Existing methods for producing fertilizer granules from inorganic materials often result in inconsistent grain sizes and require multiple comminution units, making the process inefficient and costly, while also not effectively utilizing the capabilities of two-roll mills for high-quality granule production.
A system comprising a compacting machine, a crushing device, and multiple two-roll mills arranged in series, where each two-roll mill has a distinct gap width, allowing for progressive comminution and granulation, with optional classification devices to ensure efficient loading and output of granules within the desired size range, eliminating the need for additional comminution units like impact or hammer mills.
This configuration enables the production of high-quality fertilizer granules with consistent sizes, optimizing the use of two-roll mills for both pre-shredding and final granulation, reducing the complexity and cost of the process by minimizing the use of other comminution units and enhancing the efficiency of granule production.
Smart Images
Figure EP2023086571_26092024_PF_FP
Abstract
Description
[0001] Plant and process for the production of fertilizer granules
[0002] Description:
[0003] The invention relates to a plant and a method for producing fertilizer granules from inorganic starting material. The plant comprises at least one compacting machine in which the inorganic starting material is compacted into a slurry, thus producing a slurry from the inorganic starting material. A crushing device is arranged downstream of the compacting machine, which serves to pre-comminute the slurry. In the crushing device, the slurry is crushed or pre-comminuted into slurry pieces. These pre-comminuted slurry pieces are then crushed into granules of the desired size.
[0004] This method of producing fertilizer granules is also known as press granulation or compacting granulation. The compacting machine is preferably designed as a roller press or high-pressure roller press, in which the starting material (inorganic substances) is pressed under high pressure and compacted to create what is known as a slurry (i.e. a flat, compacted strand of material). This process step is known as press agglomeration. The slurry is pre-crushed in a mechanical crusher, and then the granules of the desired grain size are produced from these slurry pieces in further crushing units (e.g. in a two-roll mill), usually with the interposition of one or more classifications.Since the inorganic substances are initially available as relatively fine-grained materials, which in this form are not suitable for mechanical spreading onto the areas to be fertilized, the described press granulation produces fertilizer granules with a defined grain size that can be handled perfectly. The goal is generally to produce fertilizer granules with a grain size of 1 mm to 5 mm. The inorganic substances used in the invention for the production of fertilizer granules can be, for example, mineral substances or substances obtained from the evaporation of salt water, e.g., chlorides or sulfates, in particular potassium sulfate or potassium chloride. Complex fertilizers, e.g., NPK fertilizers, are also included.
[0005] In the processes and systems described, a distinction must be made between a roller press on the one hand and a two-roller mill on the other. In the roller press, the starting material is compacted into the slurry under high pressure and with relatively low peripheral speeds of the rollers. The two-roller mill is used in a downstream process step to crush the slurry pieces that are produced from the slurry after compaction, e.g. with the help of a roller crusher. In contrast to roller presses, two-roller mills operate at a relatively high peripheral speed and the material is scattered loosely into the roller gap as a film of material. The roller surfaces of the two-roller mills are profiled, i.e. the roller surfaces are usually structured. A distinction must therefore also be made between the two-roller mill on the one hand and crushing devices on the other.In contrast to a crusher with a multitude of crushing elements (e.g., teeth) that act individually or in small numbers on the feed material and crush it, comminution in a two-roller mill occurs between the grinding surfaces, which may be structured, but without any specific impact of individual crushing elements on the particles to be crushed. In a crusher, comminution therefore occurs (essentially) through impact and shear stress, while in a mill (essentially) through compression and shear stress.
[0006] The compaction of inorganic substances in a roller press is known, for example, from DE 28 24 827 B2, DE 38 02 173 C1 and DE 17 58 978.
[0007] A plant and a process of the type described above are described in DE 10 2020 131 638 A1. The slurry is first crushed into slurry pieces in a crusher and / or a hammer mill. These slurry pieces are then fed to the two-roll mill, possibly with the aid of a classifying stage. The surfaces of the grinding rollers of the two-roll mill are cooled during operation.
[0008] In practice, when producing fertilizer granules using a two-roll mill, it is common practice not to feed the slugs emerging from the slug crusher directly into the two-roll mill. Instead, the slugs are first crushed in another comminution device, e.g., an impact crusher or impact mill and / or a hammer mill. Only the particles emerging from the impact mill or hammer mill are finally fed to the two-roll mill. In these systems, the two-roll mill therefore serves as the "final" comminution unit for producing the final product with the desired grain size, since the grain size can be easily adjusted using the variable gap width of the two-roll mill.
[0009] Incidentally, EP 3 801 909 B1 discloses a milling system with several mills for the industrial production of milled products. In a multi-roll mill, several pairs of rollers can be arranged one below the other, and several processing lines can also be implemented in parallel. The primary focus is on the milling of grain.
[0010] Finally, DE 16 67 147 B1 describes the granulation of fine-grained materials by pressing with roller presses and the subsequent comminution by means of impact or hammer mills as well as the classification by means of classification devices.
[0011] Further systems and processes for comminuting material are known, for example, from CN 210058412, DE 69 904 770 and GB 1 050 158 A.
[0012] Based on the prior art, the invention seeks to create a plant capable of economically producing high-quality fertilizer granules. Furthermore, a corresponding process is to be provided.
[0013] To achieve this object, the invention teaches a system having the features of patent claim 1 and a method having the features of patent claim 9.
[0014] A plant for the production of fertilizer granules with
[0015] - a compacting machine (e.g. a high-pressure roller press) for producing a slurry of inorganic starting material,
[0016] - a crushing device for pre-crushing the slugs into slug pieces,
[0017] - at least two two-roller mills arranged one behind the other in the direction of production, wherein the two-roller mills each have two rotatingly driven grinding rollers, the roller surfaces of which are provided with a profile and between which a roller gap with a (preferably adjustable) gap width is formed, wherein the flake pieces can be successively fed onto the two-roller mills arranged one behind the other for comminution into granules and wherein the gap widths of the two-roller mills are differently dimensioned or differently adjusted and decrease in the direction of production from two-roller mill to two-roller mill.
[0018] The plant can have at least one first two-roller mill arranged downstream of the crushing device and one second two-roller mill arranged downstream of the first two-roller mill, wherein the gap width of the second two-roller mill is dimensioned or set smaller than the gap width of the first two-roller mill.
[0019] Alternatively, a system can be implemented with, for example, three two-roller mills or at least three two-roller mills, with a third two-roller mill arranged downstream of the second two-roller mill, the gap width of the third two-roller mill being dimensioned or set smaller than the gap width of the second two-roller mill. Of course, embodiments with more than three two-roller mills, e.g., with four or more two-roller mills, are also feasible.
[0020] The invention is based on the finding that the use of two-roller mills in the production of fertilizer granules has proven extremely successful, since the design and functioning of the two-roller mills generally allows for the production of high-quality fertilizer granules. According to the invention, however, the two-roller mill is not only used - as is usual in the prior art - as the final comminution unit for producing the end product, i.e. not only is a two-roller mill used in the last process step, the gap width of which is adjusted to the dimensions of the end product, but according to the invention, several two-roller mills, e.g. two or three two-roller mills, are connected in series, so that, for example, the first two-roller mill is used as a pre-comminution unit for the slug pieces, i.e.The slugs emerging from the crushing device are not pre-crushed in other or additional crushing units before reaching the two-roller mill. Instead, the two-roller mills are used to further pre-crush the slugs emerging from the crushing device, while the final product is produced by the last two-roller mill in the cascade. A particularly advantageous feature is that the gap widths of the two-roller mills can be easily adjusted, so that, for example, a first two-roller mill can be implemented or set with a relatively large gap, while the downstream and possibly last two-roller mill is set with a (significantly) smaller gap, preferably adapted to the dimensions of the final product.
[0021] In principle, it is possible to arrange the two-roller mills as a cascade directly one behind the other, e.g. directly one below the other, so that the material from the first two-roller mill directly hits the second two-roller mill and optionally a third two-roller mill, so that the end product emerges from the last two-roller mill, e.g. the second two-roller mill or the third two-roller mill. In a particularly preferred embodiment, however, the plant is additionally equipped with classification devices, e.g. screening devices. Thus, the invention optionally proposes that between the crushing device and the two-roller mill arranged downstream of the crushing device, e.g. the first two-roller mill, and / or between two two-roller mills arranged one behind the other, e.g.at least one classifying device, e.g. a screening device, is arranged between the first two-roller mill and the second two-roller mill and / or between the second two-roller mill and the third two-roller mill.
[0022] It is particularly advantageous to design the system as a closed-loop grain compacting and granulating system, in which the two-roller mills and one or more classifying devices are arranged such that the flakes successively pass through the two-roller mills and the screening devices in a closed-loop process. Examples of such a closed-loop compacting and granulating system are shown and explained in the description of the figures. By using the screening devices, the two-roller mills with different gap widths can be operated particularly effectively, because with the help of the screening devices, it is ensured that the material of the appropriate size is fed into the respective two-roller mill, so that a two-roller mill with, for example, a relatively small gap is not loaded with larger material. The use of screening devices and the implementation of closed-loop grinding systems are generally known from the state of the art.According to the invention, however, this embodiment is of particular importance because the plant comprises a plurality of two-roller mills arranged one behind the other, each of which is set with a different gap width, so that the appropriate loading of the two-roller mills is of particular importance. A plant can particularly preferably be realized in which only two-roller mills are arranged downstream of the crushing device or the slug crusher as comminution units, i.e. other comminution units (e.g. hammer mills, impact mills or the like) are preferably dispensed with downstream of the slug crusher. Instead, the slug pieces emerging from the slug crusher are preferably comminutioned exclusively by the plurality of two-roller mills arranged one behind the other, so that particularly effective granulation is achieved based on two-roller mills with adjustable gap widths.Please also refer to the character description.
[0023] The specific design and construction of two-roller mills can generally be based on the findings of the prior art. Preferably, two-roller mills are equipped with two counter-rotating grinding rollers, the surfaces of which have a ribbing formed by a plurality of groove-shaped depressions and projections extending across the roller width and oriented, for example, parallel or obliquely to the roller axis, or in a spiral or arcuate configuration. It is possible to provide the two rollers with differently designed ribbing, although a spiral or arcuate configuration is generally provided on only one of the rollers.
[0024] The roller gaps of the two-roll mill can be dimensioned to a gap width in the range of 0.5 mm to 30 mm, e.g., 0.5 mm to 15 mm, and can be specifically adjusted to the desired gap width depending on the system design. Two-roll mills can also be used whose grinding rollers are equipped with cooling devices for cooling the roller surfaces. For example, two-roll mills known from DE 10 2020 131 638 A1 can be used.
[0025] The invention relates not only to the described plant, but also to a process for producing fertilizer granules from inorganic starting material, preferably using a plant of the described type. The starting material is compacted into a slurry in a compacting machine, and the slurry is pre-crushed into slurry pieces in a crushing device. The slurry pieces are crushed into granules in at least two two-roll mills arranged one behind the other. The two-roll mills arranged one behind the other are dimensioned or set with different gap widths, and the gap widths decrease from two-roll mill to two-roll mill, so that the material successively passes through several two-roll mills with decreasing roller gaps. The last two-roll mill arranged in the cascade is preferably adjusted to the dimensions of the granules to be produced.Particularly preferably, the shredded pieces emerging from the crushing device are subsequently crushed exclusively in the multiple two-roller mills, without any further shredding of the shredded pieces taking place in other upstream or downstream shredding units (such as impact mills, hammer mills, or the like). Consequently, shredding units other than two-roller mills are preferably omitted downstream of the shredded piece crusher, so that in a preferred embodiment, the invention utilizes exclusively the advantages of two-roller mills.
[0026] Independently of this, however, additional classification devices can be provided, i.e., the slug pieces are preferably classified between the crushing device and the two-roller mill arranged downstream of the crushing device and / or between two two-roller mills arranged one behind the other, e.g., using one or more screening devices. The screening devices can utilize designs known from the prior art, e.g., screening devices with one screen deck and / or screening devices with two, three, or more screen decks, so that classification into two or more fractions can take place in the screening devices.
[0027] The two-roll mills, which are of particular importance in the context of the invention, are preferably operated at circumferential speeds of at least 5 m / s, for example 5 to 30 m / s or 5 to 25 m / s, preferably 6 to 20 m / s or optionally 6 to 15 m / s.
[0028] The surfaces of the grinding rollers can be cooled during operation. The grinding rollers can have a diameter of 200 mm to 1000 mm, preferably 400 mm to 800 mm, for example 500 mm to 700 mm.
[0029] The two-roll mills can (each) rotate at a speed or speeds of 100 to 3000 rpm, preferably 120 to 1000 rpm, e.g. 150 to 800 rpm.
[0030] For diameters of 200 mm to 1000 mm and a peripheral speed of 5 to 30 m / s, the speed is 100 to 2860 rpm. For diameters of 200 mm to 1000 mm and a peripheral speed of 6 to 20 m / s, the speed is 110 to 1910 rpm.
[0031] For diameters of 400 mm to 800 mm and peripheral speeds of 5 to 30 m / s, the rotational speed is 120 to 1400 rpm. For diameters of 400 mm to 800 mm and peripheral speeds of 6 to 20 m / s, the rotational speed is 140 to 950 rpm.
[0032] For diameters of 500 mm to 700 mm and peripheral speeds of 5 to 30 m / s, the speed is 140 to 1100 rpm. For diameters of 500 mm to 700 mm and peripheral speeds of 6 to 20 m / s, the speed is 160 to 760 rpm.
[0033] It is possible to operate all two-roller mills within the system at the same peripheral speed or rotational speed and / or to dimension them to the same size. However, it is also preferably possible to dimension and / or operate the two-roller mills differently within the system, e.g., at different rotational speeds.
[0034] In any case, the two-roller mills implemented within the plant are operated with different gap widths. The roller gaps are each set to a gap width of 0.5 mm to 30 mm. It may therefore be expedient to set the gap width of the first two-roller mill to a gap between 10 mm and 30 mm and the roller gap of the second two-roller mill to a gap width of 0.5 mm to 7 mm. If three two-roller mills are implemented in series, a similar gradation can be achieved. For example, with three two-roller mills arranged in series, it may be expedient to set the roller gap of the first two roller mills to 10 mm to 30 mm and the roller gap of the second two-roller mill to 5 mm to 15 mm, as well as the roller gap of the third two-roller mill to 0.5 to 5 mm.The invention also encompasses embodiments with more than three two-roll mills arranged one behind the other, e.g., with four or more two-roll mills. In such cases, a suitable gradation of the roll gaps is also provided.
[0035] Two-roller mills are therefore of particular importance within the scope of the invention, specifically in combination with a compacting machine, which is preferably designed as a roller press. The roller press is therefore to be distinguished from a two-roller mill. A roller press for the press agglomeration of fertilizers has two counter-rotating and driven press rollers or compacting rollers that form a roller gap, whereby the starting material is pressed in the roller press under high pressure and compacted in the process, so that the slurry is created. The roller press is preferably operated with a pressing force of 40 kN to 100 kN per centimeter of roller width. The peripheral speed of the press rollers of the roller press is generally 0.3 to 1.8 m / s, and the roller diameter can be, for example, 0.5 to 1.5 m. The roller width of the press rollers is selected depending on the diameter and the desired throughput.
[0036] The invention is explained in more detail below with reference to drawings which merely represent exemplary embodiments without limiting the scope of protection.
[0037] Fig. 1 shows a schematically simplified view of a plant according to the invention for producing fertilizer granules in a first embodiment,
[0038] Fig. 2 shows a second embodiment of the invention, Fig. 3 shows a third embodiment of the invention and
[0039] Fig. 4 shows an example of a two-roll mill that can be used in a plant according to the invention.
[0040] The figures each show a plant for producing fertilizer granules in different embodiments. The plant has a compacting machine 1 for producing a slug from inorganic starting material. The compacting machine is preferably a high-pressure roller press 1, with which the inorganic starting material A is compacted into a slug S, i.e. into a flat strand of material that emerges from the nip of the roller press 1. Downstream of the roller press 1 is a breaking device 2, with which the slug S emerging from the roller press 1 is pre-crushed into slug pieces P and consequently into lumpy material with relatively large and non-uniform dimensions. This breaking device 2, which is also referred to as a slug breaker, is equipped with a plurality of breaking elements, e.g. teeth, which act individually or in small numbers on the feed material and break it up.
[0041] In all embodiments, several two-roller mills 3a, 3b, 3c are arranged downstream of the slug breaker 2, so that the lumpy material P passes successively through several two-roller mills after exiting the slug breaker. This applies to all embodiments shown in Figs. 1, 2, and 3.
[0042] The basic structure of a two-roller mill 3a, 3b, 3c is shown in Fig. 4. The two-roller mill 3a, 3b, 3c has two counter-rotating grinding rollers 7, the roller surfaces of which are provided with a profile, which is designed, for example, as a corrugation with a plurality of groove-shaped depressions and projections. These groove-shaped depressions and projections (not shown) extend across the entire roller width and are oriented, for example, obliquely to the roller axis. Each of the rollers 7 can consist of a rotatingly driven roller core and a ring band mounted on the roller core, which in turn is provided with the profile. The rollers 7 can each be equipped with a cooling device with which the roller surfaces can be cooled. Details are not shown in Fig. 4. However, Fig. 4 shows that the two-roller mills are provided with a housing 8 that forms an enclosure.Furthermore, a feed chute 9 is provided through which the material is fed. This chute 9 can be part of the housing 8 or the enclosure. In contrast to the feed to a high-pressure roller press, the material is scattered loosely into the roller gap like a curtain of material without pressure. For this purpose, a vibrating chute 5 or vibrating platform (not shown in Fig. 4) can be provided, via which the material enters the chute above the roller gap and is guided from there into the roller gap of the two-roll mill.
[0043] According to the invention, in the systems described, not only is a single such two-roller mill used as the last comminution unit for producing the end product, but several two-roller mills are provided in each case, through which the material or at least part of the material passes successively during the production process, i.e. the flake pieces P emerging from the flake breaker 2 are successively fed onto the two-roller mills 3a, 3b or 3c arranged one behind the other, wherein the gap widths of the two-roller mills within a system are differently dimensioned or set differently and preferably decrease in the production direction from two-roller mill to two-roller mill. Furthermore, in the embodiments according to Figs. 1 and 2, several classifying devices 4a, b, c are integrated into the system, namely screening devices in the exemplary embodiment.1 and 2 are each designed as circulating grain compacting and granulating systems, ie the two-roller mills and the classifying devices 4a, 4b, 4c are arranged and interconnected in such a way that the material successively passes through the two-roller mills 3a, 3b, 3c and the screening devices 4a, 4b, 4c in a circuit until the finished granulate E emerges from the last two-roller mill 3b or 3c.
[0044] This will first be explained using the system shown in Fig. 1 as an example.
[0045] The inorganic starting material A is fed, for example, via a conveying device, for example a bucket elevator 6, into the high-pressure roller press 1, in which it is compacted into the slurry S. The slurry S is then crushed into slurry pieces P in the slurry crusher 2. In the embodiment according to Fig. 1, two two-roller mills 3a, 3b are arranged downstream of the slurry crusher 2, through which the material passes successively in the sense of a circulating grinding system. For this purpose, the slurry pieces P are fed - optionally via a further bucket elevator 10 - to a first screening device 4a, which is equipped with a screen deck. The coarse fraction, i.e. the oversize grain, is fed, for example, via a vibrating chute 5 to the first two-roller mill 3a, which is set to a first gap width. The material emerging from the first two-roller mill 3a is fed back into the first screening device 4a in the circuit.
[0046] The undersize grain emerging from the first screening device 4a, and consequently the finer material, is fed to a second screening device 4b, which in the exemplary embodiment is designed for classification into three fractions. The oversize grain from the second screening device 4b is fed via a second vibrating chute 5 onto the second two-roll mill 3b, and from there it is circulated back to the first screening device 4a. The middle fraction from the second screening device 4b is discharged as the final product and consequently as granulate E of the desired size. The finest starting material F, and consequently the undersize grain from the second screening device 4b, is fed back into the production process, i.e., it is fed back to the two-roll press 1 for compaction with the starting material A.
[0047] It is therefore clear from Fig. 1 that at least a portion of the material after the slug breaker 2 is fed via the first screening device 4a to the first two-roller mill 3a and that the material comminuted therein subsequently passes through the first screening device 4a and is partially fed to the second two-roller mill 3b via the second screening device 4b, so that it then passes through both the first screening device 4a and the second screening device 4b and emerges from the second screening device as medium-sized grain and is available as the end product. The two two-roller mills 3a, 3b are therefore arranged one behind the other in the circulation process. However, this does not preclude some of the material from the slug breaker 2, namely sufficiently fine material that is already being produced, from passing through the first screening device 4a and being fed directly to the second two-roller mill 3b via the second screening device 4b.Likewise, there are material fractions that emerge from the slug breaker 2 so fine that they are already screened out as end product E in the second screening device or fed back to the roller press 1 as return material F. However, this does not change the fact that a significant portion of the material passes through the two two-roller mills 3a, 3b successively in the circuit. It is important that in the embodiment according to Fig. 2 - as in the other embodiments too - only two-roller mills 3a, 3b are provided as additional comminution units downstream of the slug breaker 2, i.e. as soon as slug pieces P are available, no other comminution units other than two-roller mills are used in the production process. Another advantage is that the gap widths of the two-roller mills 3a, 3b can be individually adjusted.The gap width of the first two-roller mill 3a, 3b is set larger than the gap width of the second two-roller mill 3b, since the first two-roller mill 3a serves for further pre-shredding, i.e. the first two-roller mill 3a is primarily intended to process and pre-shred relatively large flake pieces, so that material exits the first two-roller mill 3a that is still (significantly) larger than the final product. The gap width of the second two-roller mill 3b is set so that granules of the size of the final product E exit the two-roller mill 3b, a, i.e. the gap width is set (significantly) smaller than the gap width of the first two-roller mill 3a. It is important that the series connection of the two-roller mills 3a, 3b and screening devices 4a, 4b ensures a targeted supply of the material suitable for the following two-roller mill, i.e.This prevents material of excessive dimensions from being fed into the second two-roller mill, which has a narrow gap width. The intermediate screening devices 4a, 4b allow the feed load to be reduced and the material size to be adjusted, allowing the individual two-roller mills 3a, 3b to be relatively small overall. The machines operate particularly effectively because the differences between the feed size and the discharge size, and thus the comminution ratio, are small.
[0048] The same advantages are realized in the embodiment according to Fig. 2, in which three two-roller mills 3a, 3b, 3c are connected in series, namely a first two-roller mill 3a, a second two-roller mill 3b, and a third two-roller mill 3c. Accordingly, a first screening device 4a, a second screening device 4b, and a third screening device 4c are also implemented. The material passes successively through the screening devices 4a, 4b, 4c and the two-roller mills 3a, 3b, 3c in the manner already described. The final product exits the third screening device 4c as the middle fraction and consequently as a medium-sized particle. With this design with three two-roller mills, the respective gap width of the individual mills can be adapted even more precisely to the material to be processed, so that the individual two-roller mills are only supplied with material sizes that are suitable for particularly effective operation of the respective two-roller mill 3a, 3b, 3c.The intermediate screening devices 4a, 4b, 4c also reduce the feed load and adjust the feed size perfectly, so that relatively small machines can be used.
[0049] A modified embodiment of the invention is shown in Fig. 3. In this system, too, several two-roller mills 3a, 3b, 3c are arranged one behind the other, namely three two-roller mills in the exemplary embodiment. However, in this simplified embodiment, intermediate screening devices are omitted. The material passes from the slug breaker 2 to the first two-roller mill 3a, from there to the second two-roller mill 3b and finally to the third two-roller mill 3c, thus creating a cascade of three two-roller mills arranged one behind the other. The gap widths are graduated such that only material smaller than the desired maximum granulate size, e.g., no larger than 4 mm, emerges from the third two-roller mill 3c.Since it cannot be prevented that even the finest material, which cannot be used as granules, emerges from the third two-roller mill, a screening device 4a is also connected downstream of the cascade of several two-roller mills in this embodiment, so that only the upper grain is used as granules and consequently the end product E, while the finest material passed through the screening device 4a is fed back into the process with the starting material A and consequently into the roller press 1. In this embodiment, too, only two-roller mills 3a, 3b, 3c are provided as comminution units downstream of the slug crusher 2.
[0050] Fig. 3 is characterized by a particularly simple design, as it dispenses with screening devices between the comminution units. However, the embodiments shown in Figs. 1 and 2 are distinguished from the embodiment shown in Fig. 3 by the previously described advantage that the feed load on each two-roller mill is reduced and the material fed into each two-roller mill is well adapted to the respective gap width, so that the machines operate effectively and flawlessly and can be dimensioned accordingly small.
[0051] As mentioned, Fig. 1 shows an embodiment with two two-roller mills 3a, 3b arranged one behind the other, and Figures 2 and 3 show embodiments with three two-roller mills 3a, 3b, 3c arranged one behind the other. The invention also encompasses embodiments with four or more two-roller mills arranged one behind the other. In this case, it is also expedient to increase the number of screening devices accordingly. In Fig. 2, this is indicated schematically in a simplified manner by the symbols above the third two-roller mill 3c and above the third screening device 4c, since additional two-roller mills or screening devices can optionally be integrated at the marked locations in order to create embodiments with more than
[0052] three two-roll mills. The same applies to Fig. 3, where the symbol below the third two-roll mill 3c also shows the possibility of optionally integrating, for example, a fourth two-roll mill or even additional two-roll mills.
Claims
Patent claims: 1 . Plant for the production of fertilizer granules, with - a compacting machine (1) for producing a slug (S) from inorganic starting material (A), - a crushing device (2) for pre-crushing the slugs (S) into slug pieces (P), - at least two two-roller mills (3a, 3b, 3c) arranged one behind the other in the direction of production, wherein the two-roller mills (3a, 3b, 3c) each have two rotatingly driven grinding rollers (7), the roller surfaces of which are provided with a profile and between which a roller gap with a gap width is formed, wherein the flake pieces (P) can be fed successively onto the two-roller mills (3a, 3b, 3c) arranged one behind the other for comminution into granules (E), and wherein the gap widths of the two-roller mills (3a, 3b, 3c) are differently dimensioned or differently adjusted and decrease in the direction of production from two-roller mill to two-roller mill.
2. Plant according to claim 1 with at least one first two-roller mill (3a) arranged downstream of the crushing device (2) and one second two-roller mill (3b) arranged downstream of the first two-roller mill (3a), wherein the gap width of the second two-roller mill (3b) is dimensioned or set smaller than the gap width of the first two-roller mill (3a).
3. Plant according to claim 2, characterized in that a third two-roller mill (3c) is arranged downstream of the second two-roller mill (3b), wherein the gap width of the third two-roller mill is dimensioned or set smaller than the gap width of the second two-roller mill (3b).
4. Plant according to claim 3, characterized in that a fourth two-roller mill and optionally further two-roller mills are arranged downstream of the third two-roller mill (3c), wherein the gap width of the fourth two-roller mill is dimensioned or set smaller than the gap width of the third two-roller mill, etc.
5. Plant according to one of claims 1 to 4, wherein at least one classification device (4a, b, c), e.g. a screening device, is arranged between the crushing device (2) and the two-roller mill arranged downstream of the crushing device, e.g. the first two-roller mill (3a), and / or between two two-roller mills arranged one behind the other, e.g. between the first two-roller mill (3a) and the second two-roller mill (3b) and / or between the second two-roller mill (3b) and the third two-roller mill (3c).
6. Plant according to one of claims 1 to 5 in the embodiment as a circulating grain compacting and granulating plant, in which the two-roll mills (3a, 3b, 3c) and one or more classifying devices (4a, 4b, 4c) are arranged such that the flake pieces (P) pass through the two-roll mills (3a, 3b, 3c) and the screening devices (4a, 4b, 4c) at least partially successively in the circuit.
7. Plant according to one of claims 1 to 6, characterized in that that the surfaces of the grinding rollers (7) of the two-roll mills (3a, 3b, 3c) have a corrugation which is formed by a plurality of groove-shaped depressions and projections which extend across the roller width and are oriented, for example, parallel or obliquely to the roller axis or spirally or arcuately in one or both rollers.
8. Plant according to one of claims 1 to 7, characterized in that the roller gaps of the two-roll mills (3a, 3b, 3c) are each dimensioned or adjusted to a gap width in the range between 0.5 mm and 30 mm.
9. Plant according to claim 8, characterized in that in a plant with two two-roller mills (3a, 3b) the gap width of the first two-roller mill (3a) is set or dimensioned to 10 mm to 30 mm and the gap width of the second two-roller mill (3b) to 0.5 mm to 7 mm or that in a plant with three two-roller mills the gap width of the first two-roller mill (3a) is dimensioned or set to 10 mm to 30 mm, the gap width of the second two-roller mill (3b) to 5 mm to 15 mm and the gap width of the third two-roller mill (3c) to 0.5 mm to 5 mm.
10. Plant according to one of claims 1 to 9, characterized in that the grinding rollers (7) of the two-roller mills (3a, 3b, 3c) or at least one two-roller mill are each equipped with a cooling device for cooling the roller surfaces.
11. A process for producing fertilizer granules from inorganic starting material (A), with a plant according to one of claims 1 to 10, wherein the starting material (A) is compacted in a compacting machine (1) to form a slug (S), wherein the slurry (S) is pre-crushed into slurry pieces (P) in a crushing device (2) and wherein the slurry pieces (P) are crushed into granules (E) in at least two two-roller mills (3a, 3b, 3c) arranged one behind the other, wherein the two-roller mills (3a, 3b, 3c) arranged one behind the other are dimensioned or set with different gap widths and the gap widths decrease from two-roller mill to two-roller mill.
12. The method according to claim 11, wherein the comminution of the flake pieces (P) takes place exclusively in the plurality of two-roll mills (3a, 3b, 3c) without further upstream or downstream comminution units.
13. The method according to claim 11 or 12, wherein a classification of the slug pieces, e.g. with one or more screening devices (4a, 4b, 4c), takes place between the crushing device and the two-roll mill (3a) arranged downstream of the crushing device (2) and / or between two two-roll mills (3a, 3b, 3c) arranged one behind the other.
14. The method according to claim 13, wherein the material is circulated by preferably feeding the material emerging from a two-roll mill (3a, 3b, 3c) to a screening device (4a, b, c).
15. Method according to one of claims 11 to 14, wherein the surfaces of the grinding rollers (7) are cooled during operation.
16. The method according to any one of claims 11 to 15, wherein the grinding rollers (7) rotate at a peripheral speed or at peripheral speeds of at least 5 m / s, e.g., 5 to 30 m / s, e.g., 5 to 25 m / s, preferably 6 to 20 m / s.
17. The method according to any one of claims 11 to 16, wherein the grinding rollers (7) have a diameter of 200 mm to 1000 mm, preferably 400 mm to 800 mm, e.g. 500 mm to 700 mm and / or rotate at a speed or speeds of 100 to 3000 rpm, preferably 120 to 1000 rpm, e.g. 150 to 800 rpm.
18. The method according to any one of claims 11 to 17, wherein the roller gap is set to a gap width of 0.5 mm to 30 mm, wherein preferably in a plant with two two-roll mills (3a, 3b) the gap width of the first two-roll mill (3a) is set to 10 mm to 30 mm and the gap width of the second two-roll mill (3b) is set to 0.5 mm to 7 mm or wherein in a plant with three two-roll mills the gap width of the first two-roll mill (3a) is set to 10 mm to 30 mm, the gap width of the second two-roll mill (3b) is set to 5 mm to 15 mm and the gap width of the third two-roll mill (3c) is set to 0.5 mm to 5 mm.